1. Field of the Invention
The present invention relates to a method and apparatus for providing adjustable hot runner assembly seals, as well as adjustable hot runner nozzle tip height, by utilizing active material elements in injection molding machine equipment (e.g., hot runner nozzle assemblies). “Active materials” are a family of shape altering materials such as piezoactuators, piezoceramics, electrostrictors, magnetostrictors, shape memory alloys, and the like. In the present invention, they are used to adjust the hot runner assembly seals and to adjust the nozzle tip height, thereby improving the quality of the molded article, the life of the nozzle assembly, and the resin sealing. The active material elements may also be used as sensors.
2. Related Art
Active materials are characterized as transducers that can convert one form of energy to another. For example, a piezoactuator (or motor) converts input electrical energy to mechanical energy causing a dimensional change in the element, whereas a piezo sensor (or generator) converts mechanical energy—a change in the dimensional shape of the element—into electrical energy. One example of a piezoceramic transducer is shown in U.S. Pat. No. 5,237,238 to Berghaus. One supplier of piezo actuators is Marco Systemanalyse und Entwicklung GmbH, Hans-Böckler-Str. 2, D-85221 Dachau, Germany, and their advertising literature and website illustrate such devices. Typically an application of 1,000 volt potential to a piezoceramic insert will cause it to “grow” approximately 0.0015″/inch (0.15%) in thickness. Another supplier, Midé Technology Corporation of Medford, Me., has a variety of active materials including magnetostrictors and shape memory alloys, and their advertising literature and website illustrate such devices, including material specifications and other published details.
U.S. Pat. No. 4,588,367 to Schad and U.S. Pat. No. 6,343,925 to Jenko each disclose a hot runner nozzle with a spring means for taking up thermal expansion of the assembly, in order to ensure that a good seal between the nozzle body and the hot runner manifold is maintained throughout the range of operating conditions.
U.S. Pat. No. 5,853,776 to Meijer discloses a spring means for a backup insulator. It also discloses a nozzle housing insulator and a hot runner manifold melt channel plug installation. These sealing structures suffer from being passive devices relatively incapable of being actively controlled or capable of different levels of performance.
Thus, what is needed is a new technology capable of sealing the various injection molding machine surface with fine levels of adjustable control, and preferably with embedded sensors and closed loop control of the sealing function.